1. Field of the Invention
The present invention relates to an auto white balance method using processing a digital image, and more particularly, to an auto white balance method in a YCbCr color space, the method capable of executing a white balance of an image frame detected by an image sensor by calculating R and B color gains of the image sensor by using pixels of a particular section according to Y, Cb, and Cr values among inputted image frames expressed in the YCbCr color space.
2. Description of the Related Art
In general, though a peripheral lighting environment, that is, a light source is changed, eyes of a human always recognize white as it is. For example, a white color under a blue light source such as a fluorescent lamp, a white color under a white light source, and a white color under a red light source such as an incandescent lamp are recognized as the same to eyesight of a human.
However, in the case of image sensors, detected white colors vary with peripheral light sources. That is, since image sensors reproduce a reflected light of a given color temperature, a detected white color is changed. That is, light sources have a different color temperature from one another. For example, an object of white appears red under a light source with a low color temperature and appears blue under a light source with a high color temperature. To compensate a color difference occurring due to various light sources with a different color temperature, most of image apparatuses employing an image sensor, such as digital cameras and digital camcorders, perform a digital image processing process such as white balance.
Generally, the white balance may be performed by estimating a degree of a change caused by a light source from an image obtained from an image sensor and determining a gain for each color of the image sensor to compensate the change.
As conventional auto white balance methods, there are known a maximum RGB method of estimating white based on respective maximum red, green, and blue values from an image, a grayworld method of determining average RGB values of an inputted color image as a gray color and estimating a reference white color by using the gray color, and a method of estimating a reference white color by using a nerve network. As a representative method of compensating colors of an object by using conventional estimation methods, a method of expressing a distorted white object as accurate white by controlling a color gain that is a coefficient multiplied by color information, which is called as auto white balance. Ideally, in the case of an image processed with auto white balance, colors of an image, obtained by photographing the image under all light sources, should be identical to original colors.
However, in the case of the conventional auto white balance method, there are many cases that wrong color gains are calculated by estimating wrong white color when only a certain portion of an image is very bright or a lot of certain colors are distributed. Due to this, auto white balance is not accurately performed.